The proposed investigation is a genetic and phenotypic analysis of mutants of Tetrahymena pyriformis affected in cell division and in the positioning of cell structures. We have already identified high- temperature- sensitive mutants at eight gene loci. We are proceeding with analysis of the cell-surface and nuclear phenotypes of these, employing scanning electron microscopy, silver staining, and feulgen staining with quantitative microfluorimetery( the last-mentioned a collaborative project with another research group). We also plan to analyze the time of gene action ("execution point") of those mutants that show blockage in the first cell cycle after transfer to the non-permissive temperature. Mutant cells will also be transferred back to a permissive temperature after varying period at non-permissive temperature, to analyze the degree of reversibility of the temperature induced block and the regulation of form and pattern in blocked cells. The search for new mutants will also be continued, employing both the chemical mutagen (nitrosoguanidine) that we have used thus far, and also X-ray to possibly obtain a somewhat different spectrum of mutants. Finally, we plan to screen for low-temperature as well as high-temperature-sensitive mutants, to make possible more refined studies of the sequence of gene-controlled steps, in double mutants.